A composite lead frame comprises a flexible print circuit (FPC) or a tape automated bonding (TAB) tape having an LSI mounting portion and copper foil lead patterns thereon, and a metal lead frame having inner and outer leads supported by a frame member, wherein the inner leads are connected to the copper foil lead patterns on a bonding region.
In connecting the inner leads to the copper foil lead patterns, a junction layer is interposed at each interface of the inner leads and the copper foil lead patterns. The junction layer is, for example, of a Au--Sn alloy. The connection of the inner leads and the copper foil lead patterns is carried out by the steps of mounting the copper foil lead patterns plated with Au on a work stage, placing tip portions of the inner leads plated with Sn on the copper foil lead patterns, and applying heat and pressure on the tip portions of the inner leads by a heating tool. After the heat and pressure applying step, the heating tool is cleaned to remove Sn attached thereto, because the heating tool is contaminated by Sn.
Another type of a composite lead frame comprises a flexible print circuit having inner leads on an insulation film, and a metal lead frame having outer leads supported by a frame member, wherein the inner leads and the outer leads are connected by applying heat and pressure thereto. In one case, the temperature of the heating is set to be lower than a temperature, by which the insulation film is deteriorated.
However, the former and latter composite lead frames have disadvantages in that the productivity is lowered, because the cleaning of the heating tool must be done at each time after the heat and pressure applying step is finished, and the stabilized connection of the inner and outer leads (or the inner leads and the copper foil lead patterns) is not obtained, because a plastic resin is molded to seal an integrated circuit chip mounted on the composite lead frame by a temperature higher than the temperature applyied to the inner and outer leads.